1. Field of the Invention
The present invention relates generally to a Hall effect device. In particular, the present invention relates to a hybrid Hall effect device (i.e., a magneto-electronic device) comprising a semiconductor structure and a ferromagnetic element or layer. The devices according to the present invention are useful for various applications including, but not limited to, nonvolatile random access memory array (NRAM), use as a logic gate, field effect transistor (FET), and any other sensing element in the category of Hall effect devices.
2. Description of the Background Art
The semiconductor field effect transistor (FET), typically fabricated as a metal oxide semiconductor (MOSFET) structure on a silicon substrate or gallium arsenide device (GaAsFET) on a gallium arsenide substrate, is the building block of modern digital electronics. For example, memory cells for the storage of binary information and logic gates for the processing of digital data streams both use FET""s as the primary components.
A standard representation for a classic four-terminal Hall plate is a cross centered in a square. Two opposing terminals on two opposing sides of the square are used for current bias I+ and Ixe2x88x92 (or voltage bias), and two other opposing terminals on the remaining two opposing sides are used as sensing probes for sensing a bipolar Hall voltage (or current).
Recently, certain modified Hall effect devices (i.e., a hybrid combination of a conventional Hall plate coupled to a ferromagnetic layer) have been disclosed. A modified Hall plate incorporates a ferromagnetic film that is usually fabricated to be electrically isolated from the Hall plate (e.g., by an insulating layer) but to cover a portion of the area of the Hall plate such that an edge of the ferromagnetic film is over a central region of the plate. Local, fringe magnetic fields from the edge of the ferromagnetic film are perpendicular to the plane of the plate, may point xe2x80x9cupxe2x80x9dxe2x80x2 or xe2x80x9cdownxe2x80x9d depending on the orientation of the magnetization of the ferromagnetic film, and have an average value Bav in the active region of the device. For constant bias current the sensed Hall voltage (or current) has opposite polarity when the fringe fields are xe2x80x9cupxe2x80x9dxe2x80x2 compared with when they are xe2x80x9cdown.xe2x80x9d The magnetization of the ferromagnetic film is typically in the plane of the ferromagnetic film and lies along an axis parallel with that of the bias current, but it is also possible to use a magnetic material with magnetization perpendicular to the plane. In the former case, the magnetization can have two stable states along the axis parallel with the bias current and each state corresponds to xe2x80x9cupxe2x80x9d or xe2x80x9cdownxe2x80x9d fringe fields near the edge of the ferromagnetic film, positive or negative Hall voltage (or current), and a binary bit of information xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d. The magnetization state can be set (written) to be positive or negative by using the magnetic field associated with a positive or negative current pulse transmitted down an integrated write wire that is contiguous with the ferromagnetic film, as in U.S. Pat. No. 5,652,445 (""445) to Johnson, which is incorporated herein by reference for all purposes. It follows that such a device can be used as the nonvolatile storage element in an array of elements comprising a nonvolatile random access memory (NRAM).
The ""445 patent involves an application in high density nonvolatile memory and logic gate environments. The ""445 patent involves a conductive film layer, a ferromagnetic layer, a fringe magnetic field, and an electrical signal. Reference is also made to the ""445 patent for further discussion of the Hall effect and other Hall effect devices.
The need exists to provide new, modified Hall effect devices with further enhancements. In particular, there is a significant need in the art for improved hybrid Hall effect devices that are more reliable for use in high density memory and logic environments than existing hybrid Hall effect devices.
Accordingly, it is an object of the present invention to provide a significantly improved hybrid Hall effect device that exhibits increased reliability in high density memory and logic environments.
It is also an object of the present invention to present novel materials systems to be used in the fabrication of hybrid Hall effect devices, with the effect of enhancing the operating speed and increasing the output signal level of the device.
It is another object of the present invention to provide a substantially improved hybrid Hall effect device in which the remanence of the magnetic component layer is larger and therefore the bistable output voltage (or current) is larger.
It is yet another object of the present invention to achieve a further improvement over existing hybrid Hall effect devices by providing devices with a square hysteresis loop of the ferromagnetic component, thereby improving the efficiency of the write process.
It is a further object of the present invention to achieve an improvement over existing hybrid Hall effect devices by providing devices with a lower coercivity of the ferromagnetic component, thereby lowering the power of the write process.
It is another object of the present invention to achieve a further improvement over existing hybrid Hall effect devices by providing devices in which the perpendicular component of magnetic field is increased in the active region of the device, thereby increasing the output voltage (or current).
It is also an object of the present invention to achieve a further improvement over existing hybrid Hall effect devices by providing devices with decreased switching time of the ferromagnetic component layer.
It is also an object of the present invention to achieve a further improvement over existing hybrid Hall effect devices by providing devices with novel materials systems that have high mobility and produce larger output voltages (or currents).
It is yet another object of the present invention to achieve a further improvement over existing hybrid Hall Effect devices by providing devices incorporating novel materials systems that are compatible with the fabrication requirements of the support circuitry, such as select, sense and amplification circuits.
These and other objects of the invention are accomplished by providing a Hall effect device comprising:
(a) an electrically-conductive layer or plate having a top surface and capable of carrying an electrical current;
(b) a ferromagnetic layer comprising a material selected from the group consisting of: (i) ferrites and (ii) perovskite ferromagnetic oxides; and
(c) where an electrical signal can be generated in response to the fringe magnetic field acting on the electrical current.
In another embodiment, the objects of the present invention are achieved by providing a Hall effect device comprising:
(a) an electrically conductive layer or plate having a top surface; and
(b) a ferromagnetic multilayer comprising at least a first magnetic layer and a second magnetic layer.
In yet another embodiment of the present invention, the objects of the present invention are achieved by a Hall effect device comprising:
(a) an electrically-conductive layer or plate having a top surface; and.
(b) a ferromagnetic layer,
(c) where the electrically conductive layer or plate comprises an indium compound or a germanium compound.
Thus, in one aspect, it has been discovered that certain classes of ferromagnetic materials (e.g., ferrites or perovskite ferromagnetic oxides) can be used for the fabrication of modified Hall effect devices to achieve faster switching times.
In addition, it has been discovered that the ferromagnetic layer can be fabricated as one component of a multilayer (e.g., bilayer), where the second component is a thin magnetic (ferromagnetic or antiferromagnetic) layer for magnetically biasing the first layer. The result of the magnetic bias can be a larger remanence and/or a hysteresis loop that is not symmetric with respect to zero applied field. Other optional layers in the multilayer include, but are not limited to, buffer layer(s) for improving the quality of growth of the ferromagnetic layer and/or bias layer or a passivation layer for protecting the multilayer from environmental degradation.
Furthermore, it has been discovered that a shape anisotropy can be employed to reduce the coercivity (and therefore reduce the amplitude of current in the write pulse) of the ferromagnetic component, and that an additional element can be used to close flux lines and alter the perpendicular field component in a desirable way. For example, to provide a higher concentration of flux, to prevent stray flux from affecting other parts of the device, and to provide a more perpendicular orientation of the lines of the flux.
Additionally, in considering the class of semiconducting materials used to fabricate the Hall plate, it has been discovered that several different semiconducting materials, with mobilities larger than those of silicon or gallium arsenide, can be used to achieve larger readout voltages (or currents).